Although eggs represent an outstanding nutritional food which is enjoyed by many people, especially as part of one's breakfast, the fact is that natural egg yolk is one of the richest foods in cholesterol. This has forced a large number of people who are on cholesterol and fat free diets from enjoying eating natural whole eggs. One practical and economically feasible solution has been to incorporate a simulated and preferably a cholesterol free egg yolk into natural egg white and to preserve them in separate phases, so that one can make, for example, a "sunny side up" and "over easy" egg. In this regard, there is known in the inventor's U.S. Pat. No. 5,073,399, which is incorporated by reference herein, a simulated egg yolk and simulated raw whole egg manufactured therewith constituting an edible liquid, a viscosity modifier which is preferably a positive thermoreversible gel former, and a colorant. The simulated egg yolks produced thereby, which may be encapsulated by a hydrocolloid restrictive barrier, are remarkably lifelike and are useful in the preparation of "sunny side up" and "over easy" eggs when disposed in natural egg whites.
The inventor realized that in the preparation of a simulated whole raw egg for use in the production of a natural looking "sunny side up" or "over easy" egg, it is typically necessary to store the simulated egg yolk in a separate gelled phase within liquid natural egg white. It was observed that these simulated egg yolks tend to absorb water from the natural egg white, probably by osmosis, thereby undesirably increasing the weight and volume of the egg yolk. The absorption of water is undesirable because it decreases the viscosity of the egg yolk upon cooking, which adversely results in the reduction of the egg yolk's overall mechanical and/or physical strength, i.e., the ability to remain unbroken and to retain its integrity and shape prior to being purposefully broken after cooking when being eaten. The decrease in viscosity can result in the premature disruption of the structure of the discrete egg yolk when in the molten state, such as during cooking, and uncontrolled running of the egg yolk at serving temperatures may take place. In addition, the reduction in the egg yolk's mechanical and/or physical strength requires that the egg yolk be handled delicately.
In the inventor's U.S. Pat. No. 5,151,293, which is also hereby incorporated by reference, a number of possible remedies to overcome these problems of water absorption were proposed. It was observed that the positive thermoreversible gel former used in the production of the simulated egg yolk appeared to be the driving force behind the absorption of water from natural egg white. Although it was proposed to minimize the amount of gel former used, this also had the tendency of producing "delicate" egg yolks whose viscosity will change prematurely such that the egg yolk's monolithic structure is lost during manufacturing and/or handling, including during cooking. Thus, the proposed solution created other problems which were not fully resolved.
Another proposed method of reducing the initial weight gain of a simulated egg yolk, yet maintaining its viscosity and mechanical and/or physical strength, is by the use of a restrictive barrier. Several methods of imparting such a barrier to the egg yolk before being added to liquid natural egg white are described, such as a cross-linked membrane of an edible resin, e.g. an alginate, a pectin, and the like. A multivalent cation, such as calcium or aluminum in the form of a salt may be used as the cross-linking agent. A restrictive barrier can also be formed from hydrateable edible polymeric compounds or hydrocolloids which give rise to substantial instantaneous increase in viscosity as soon as they come into contact with and start dissolving in aqueous systems.
Also disclosed is reducing the absorption of water by adding a solute to the liquid egg white such that smaller osmotic pressure differential will exist between the liquid egg white and the simulated egg yolk. This is expected to minimize the force thought to be driving water into the egg yolk. Finally, the inventor proposed immersing the egg yolk in an aqueous medium which provides an accelerated tendency of the egg yolk to absorb water. In this technique, the egg yolk is formulated with less water than would otherwise be used. The egg yolk is then immersed into water until the degree of water absorption desirable has been achieved. When added to liquid egg white, the thus created egg yolk does not exhibit a strong tendency to further absorb water.
Although the '293 patent mentions forming a restrictive barrier layer from a cross-linked film of an edible resin, there is no reference to a particular method of forming the barrier around an egg yolk. The methods used so far to produce restrictive barriers around simulated egg yolks were both time consuming and cumbersome. For example, Forkner, U.S. Pat. No. 4,409,249, discusses briefly the use of cross-linked hydrocolloids, such as alginates, with calcium salts, as edible membranes around artificial liquid yolks to hold the shape of the egg yolk. Cox et al., U.S. Pat. No. 5,192,566, discloses various detailed methods of forming a restrictive barrier around a simulated liquid egg yolk. In both Forkner and Cox et al. frozen or otherwise immobilized liquid egg yolk is coated with a restrictive barrier forming solution or dispersion such as one containing edible hydrocolloids, for example, sodium alginate. The coated egg yolk is treated to form the restrictive barrier by contact with a reactive composition in the form of a setting bath containing a setting agent, for example, calcium chloride. Cox et al. discusses two alternative methods, the first of which they co-extrude a central yolk portion with a surrounding portion containing the film former, and in the second they include the film former in the formulation of the yolk. In the preferred method of Cox et al., the second method, the restrictive barrier forming compounds are mixed with the egg yolk components in sufficient quantities to form a barrier on the outer surface of the egg yolk when contacted with a setting agent. The liquid egg yolk is extruded in the form of discrete liquid globules into a setting bath. These methods are undesirably time consuming, requiring the yolks to stay in the setting bath for 8-15 minutes, followed by rinsing for about 10-20 minutes.
This conventional process of forming a restrictive barrier in accordance with either Cox et al. or Forkner was found to present a large number of disadvantages resulting in a simulated egg yolk having a poorly formed barrier. A major drawback is the commercially undesirable (which may come to the point of being unacceptable) length of time needed to complete the process. When attempting to use reasonably short times for the conventional process, additional drawbacks, just to mention a few, include, but are not limited to, irreproducibility of the quality of the membrane, thickness variability, openings in the membrane structure, weak regions which may break easily, and tough to chew regions making the consumption of the respective egg unpleasant.
More particularly, the coating of the egg yolk first with a restrictive barrier forming compound often results in a barrier which is not only flimsy, but also not uniform in thickness. When immersed in the setting bath, the restrictive barrier forming compound often does not cross-link uniformly, in particular, in those regions having a thicker layer, thereby requiring extended residence times. In addition, it has been found that in those regions where an excess of restrictive barrier forming compound is present, incomplete cross-linking may still occur, resulting in the barrier layer being relatively weak, and in fact, may be in the nature of a loose slurry. These regions are potential defect sites which can cause the simulated egg yolk to prematurely rupture during handling.
The setting bath which contains the setting agent, for example, calcium chloride being the major representative of setting agent, even at small concentrations is known to have a bitter taste. Any excess setting agent which is retained on the egg yolk will subsequently dissolve in the liquid egg whites into which the egg yolk is deposited. This will result in the finally cooked whole egg having a bitter unpleasant taste which is unacceptable to the consumer. To avoid this problem, it becomes necessary to subsequently subject the egg yolk to an extensive rinse bath which is highly undesirable from the standpoint of both process time and economy.
A further disadvantage is the high probability of a remaining slippery fluid region under the membrane and surrounding the solid at room temperature yolk portion, which fluid region consists of unset or incompletely set film former. All these disadvantages render these processes very delicate, sensitive to unforeseen external parameters, time consuming, and cumbersome. Still more particularly, according to the conventional method, the yolk is dipped into a solution of a film former, which is very viscous even at low concentrations of film former, and therefore it produces an uneven thick film on the yolk. When this film comes in contact with the solution of the setting agent, a thin cross-linked skin is formed at the top of the film, away from the yolk. The skin does not allow easy access to the rest of the trapped film former, and thus, one has to wait for a long time (many minutes) for the setting agent, for example calcium ions, to diffuse through the skin and continue setting the rest of the resin. This increases the thickness of the skin and makes the diffusion process more and more difficult. If one does not wait for all the time required to complete the setting throughout the thickness of the film, there will remain a slippery fluid region under the skin, adjacent to the yolk, rendering the thus far made membrane flimsy and not supported by the non-flowable yolk. Further, since the outermost skin of the membrane will be fully cross-linked, due to the abundance of setting agent in that region, its adhesion to the white will be minimal, if any at all, upon cooking the yolk and coagulating the white. It is a very well known fact that fully cross-linked surfaces are notorious for refusing to adhere to other surfaces, and they may even be used as release structures. Thus, special treatment will be needed to provide adhesion of the membrane to the white.
Since the environment at which the membrane was formed in this case includes an abundance of setting agent, thorough rinsing becomes necessary in order to remove the setting agent (calcium chloride, for example) before the processed yolk is introduced into the egg white. The task of removing the setting agent becomes even more difficult, due to the fact that the portion of setting agent which has been trapped within the fully cross-linked outer part of the membrane, and which travels outward at a very low speed, does not find any uncross-linked sites to be bound, and therefore it has to be substantially removed completely to avoid the undesirable taste and other ailments that may introduce to the white.
Neither of the aforementioned patents provide a commercially feasible method of manufacturing large quantities of high quality simulated egg yolk and "friable" (either "sunny side up" or "over easy") or "poachable" whole eggs. In the case of U.S. Pat. No. 5,151,293, the problems of commercializable methods are complicated by attempting to balance the complexities of water absorption and the need for a strong, monolithic simulated egg yolk with a highly controlled temperature/viscosity profile (yolk formulated to only become runny and lose its shape when desired).
These problems were solved in Applicant's co-pending Application Ser. No. 08/075,106 filed Jun. 11, 1993 which is also incorporated herein by reference, by the provision of a commercially feasible mass production method for the formation of high quality simulated egg yolk which is extrudable at or below room temperature in accordance with the present invention. The resulting simulated egg yolk, when added to liquid natural egg white and, thereafter, fried, yields a realistic egg in flavor, texture and look. The resulting egg retains a discrete egg yolk, even at serving temperatures, which naturally runs upon being disturbed. Thus, the resulting egg product looks, tastes and behaves as a natural fried or poached egg. Applicant discloses in U.S. Pat. 5,401,525, issued on Mar. 28, 1995, which is incorporated herein by reference, an apparatus and method of performing coating of the yolks. However, the disclosed method of coating yolk disks involves many moving parts, which add complexity.